1. Field of the Invention
The present invention relates to an electroluminescent display.
2. Description of the Related Art
An electroluminescent display (EL display) is understood as a flat body which has a luminescent layer, containing at least one electroluminophore, i.e., a material which luminesces due to excitation using an electrical (AC) field, incorporated in a binder matrix, over at least part of its area. EL displays are used particularly as advertising panels having luminescent display areas. In addition, there are multiple applications as visual aids, displays, decorative elements, light fixtures, etc.
The electroluminophores or luminescent pigments are embedded in a transparent, organic or ceramic binder. The starting materials are typically zinc sulfides, which generate different, relatively narrow-band emission spectra as a function of doping and/or co-doping and preparation procedure. The focus of the spectrum determines the particular color of the emitted light.
In connection with the present application, transparent is understood as the opposite of opaque, i.e., as recognizably transparent to light and/or noticeably translucent as used in general speech. Therefore, transparent as defined here does not require light transmission of nearly 100%. A light transmission of 15% would also still be considered transparent. Only slight light transparency, i.e., a degree of transmission which solely allows light sources to glimmer through weakly, in contrast, is no longer understood as transparent.
The exciting AC voltage field typically has a frequency of a few hundred hertz, the effective value of the operating voltage frequently being in a range from approximately 50 to 150 volts. By elevating the voltage, a higher light density may normally be achieved, which is typically in a range from approximately 50 to approximately 200 candela per square meter. Elevating the frequency usually causes a color shift toward lower wavelengths. Both parameters must be tailored to one another in order to achieve a desired light impression, however.
The AC field is applied via thin planar electrodes, which are situated on both sides of the luminescent layer and are implemented as transparent at least on the viewing side. The electrodes layers form a planar luminescent capacitor together with the luminescent layer and possibly additional dielectric layers and/or color-filtering or color-converting layers.
For practical and design reasons, the luminescent layers of EL displays are usually implemented as a large number of non-coherent partial areas, which are each used as display segments and/or pixels. The individual display segments and/or pixels may be implemented in various colors and in greatly varying shapes and are referred to in general in the following as “partial image areas”. At least one of the electrodes layers is usually also implemented only in the area of the partial image areas, particularly, however, if partial image areas are to be individually activatable, for example, for movie-like effects, blinking effects, changing display texts, etc.
Typical EL displays, in particular EL displays used as advertising signs or visual aids, normally have a construction comprising two conductively coated glass or plastic panes, the luminescent capacitors being situated between the panes, which are contacted on their rear faces via carbon zebra strips, for example.
Large-area displays in particular are relatively complex to produce, since two largely rigid panes have to be handled during the manufacturing. The weight of the finished display is also significant due to the two panes.